1. Field of the Invention
The present invention relates to an ac-dc converting device for converting power supplied by an outside ac power source to charge a battery of an electric vehicle.
2. Description of the Related Art
Such an ac-dc power converting device for an electric vehicle has a rectifier for rectifying alternating current to direct current. Because the output voltage of the rectifier varies with the height of the voltage wave, a transformer is used to provide a high voltage. Since such a transformer is bulky and heavy, JP-A-7-87616 proposes a system which is composed of a circuit for rectifying the commercial ac power source to dc power and series-connected circuit of a switch and an inductor. The output power of the circuit is accumulated in the inductor while the switch is turned on, and the output voltage is raised when the switch is turned off. The system, which is proposed for an electric vehicle, uses stator windings of an ac drive motor of a vehicle in order to reduce the weight and cost of the system.
However, if the insulator of one of the stator windings of the system deteriorates, and the one of the stator windings is short-circuited to the vehicle body by accident, a dc current flows from the one of the stator windings through the vehicle body--which is grounded while the battery is being charged for safety reason. Such a dc current also flows through the grounded portion of the vehicle body, the grounded terminal of the electric source, the other terminal of the electric source, the rectifier and the one of the stator windings. This may cause the electric corrosion of the vehicle body.